iOS 开发之NSDecimalNumber 的简单应用

NSDecimalNumber

NSDecimalNumber,不可变NSNumber 的子类,提供了一个面向对象的十进制运算包装器 。实例可以代表任意数值,表示为(mantissa)尾数x 10 ^(exponent)指数,(mantissa)尾数是一个十进制整数到38位长,(exponent)指数是一个整数从-128年到127。

实例化方法如下，mantissa：长整形；exponent：指数；flag：正负数。

+ (NSDecimalNumber *)decimalNumberWithMantissa:(unsigned long long)mantissa exponent:(short)exponent isNegative:(BOOL)flag;

Example:

参数表示 一个number的科学记数法 ,要求(mantisa)尾数是一个整数。例如,如果表示的数是-15.99,它是表示为1599 x10 ^ 2 -mantissa 是12345;(exponent)指数是2;和isNegative(一个布尔值,用于指定number 的(sign)符号是负的)是YES

NSDecimalNumber *number = [NSDecimalNumber decimalNumberWithMantissa:1599
                                           exponent:-2
                                           isNegative:YES];

+ (NSDecimalNumber *)decimalNumberWithDecimal:(NSDecimal)decimal

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给定一个NSDecimal数据结构,创建并返回一个等价的 NSDecimalNumber对象

+ (NSDecimalNumber *)decimalNumberWithString:(NSString *)numericString

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创建并返回一个NSDecimalNumber对象值相当于个给定的数字字符串。
numericString:除了数字字符串,numericString可以包括一个“+”或“-”,一个“E”或“E”,用科学记数法表示一个数的指数,和一个NSLocaleDecimalSeparator划分的部分数的有效组成部分。

+ (NSDecimalNumber *)decimalNumberWithString:(NSString *)numericString  locale:(id)locale

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locale:一个字典定义语言环境(特别是NSLocaleDecimalSeparator),在进行解析numericString的时候

NSDictionary * locale = @{NSLocaleDecimalSeparator:@","];    //以","当做分隔符格式
NSDecimalNumber * discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale];    //123.4

以下是numericString的一些正确示例:

“2500.6” (or “2500,6”, 取决于 locale)
“–2500.6” (or “–2500.6”)
“–2.5006e3” (or “–2,5006e3”)
“–2.5006E3” (or “–2,5006E3”)

以下是numericString的一些错误示例:

“2,500.6”
“2500 3/5”
“2.5006x10e3”
“two thousand five hundred and six tenths”

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一个 等同于 1.0的NSDecimalNumber对象

+ (NSDecimalNumber *)one 

一个 等同于 0.0的NSDecimalNumber对象

+ (NSDecimalNumber *)zero

没有指定数值的NSDecimalNumber对象
常用于对比，比如：[[NSDecimalNumber notANumber] isEqualToNumber:myNumber];

+ (NSDecimalNumber *)notANumber

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初始化Decimal Number

一个NSDecimalNumber使用给定decimal对象初始化

 - (instancetype)initWithDecimal:(NSDecimal)decimal

使用(mantissa)尾数, (exponent)指数 number 的(sign)符号,来初始化NSDecimalNumber

- (instancetype)initWithMantissa:(unsigned long long)mantissa  exponent:(short)exponent  isNegative:(BOOL)flag

创建并返回一个NSDecimalNumber对象值相当于个给定的numericString数字字符串。

- (instancetype)initWithString:(NSString *)numericString

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以numericString,locale初始化NSDecimalNumber对象
locale:一个字典定义语言环境(特别是NSLocaleDecimalSeparator),在进行解析numericString的时候

- (instancetype)initWithString:(NSString *)numericString  locale:(id)locale

加法运算

-(NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber;
-(NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;

减法运算

-(NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber;
- (NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber withBehavior:(id<NSDecimalNumberBehaviors>)behavior

乘法运算

-(NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber;
-(NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;

除法运算

-(NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber;
-(NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;

幂运算

-(NSDecimalNumber *)decimalNumberByRaisingToPower:(NSUInteger)power;
-(NSDecimalNumber *)decimalNumberByRaisingToPower:(NSUInteger)power withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;

指数运算

-(NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power;
-(NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power 
withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;

四舍五入运算

-(NSDecimalNumber *)decimalNumberByRoundingAccordingToBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;

比较大小

-(NSComparisonResult)compare:(NSNumber *)decimalNumber;
简单应用
NSDecimalNumber *discount1 = [NSDecimalNumber decimalNumberWithString:@"2.1"];
  NSDecimalNumber *discount2 = [NSDecimalNumber decimalNumberWithString:@"2.2"];
  NSComparisonResult result = [discount1 compare:discount2];
  if (result == NSOrderedAscending) {
      NSLog(@"discount1 <discount2");
  } else if (result == NSOrderedSame) {
      NSLog(@"discount1 == discount2");
  } else if (result == NSOrderedDescending) {
      NSLog(@"discount1 > discount2");
  }

特别鸣谢

如何使用NSDecimalNumber？
‘NSDecimalNumber–十进制数’使用方法
OC : NSDecimalNumber